1. Field of the Invention
The present invention relates to guidance systems. More specifically, the present invention relates to guidance for weapons systems using the Global Positioning System (GPS).
2. Description of the Related Art
The utility of the Global Positioning System for guidance applications is well recognized. The Global Positioning System is a network of satellites that transmits information in signals, which when received and decoded, allow a receiver to accurately fix its position within a coverage area. For military applications, GPS allows self-guided weapons to find targets with heretofore unknown degrees of accuracy.
Unfortunately, GPS guidance, which uses 10 watt signals from satellites in an 11,000 nautical mile orbit, is notoriously easy to jam with low power, low cost jammers scattered around a target area. As a large number of units would be used to defend high value targets, one by one destruction of the jammers would have a low payoff. If only a few remain operational, they can effectively jam incoming weapon systems.
At least two measures are being considered to provide an anti-jamming countermeasure for GPS guided vehicles. One measure involves the use of a nulling antenna system. In accordance with this approach, the vehicle is equipped with a number of antennas which point a null in the antenna radiation pattern at the source of the jamming signal. Though somewhat effective, this approach can be expensive as the number of jammers that can be nullified is one less than the number of antenna elements. Hence, the effectiveness of this limited approach is questionable if a large number of inexpensive jammers are used.
Thus, there is a need in the art for an effective anti-jamming countermeasure for GPS guided weapon systems.